1. Field of the Invention
The present invention is directed to an electronic control for hydraulic system, and more particularly to precision control of hydraulically driven generators for stabilizing frequency and voltage output characteristics.
2. Background Art
Most engine driven vehicles utilize an internal combustion engine as the primary power source for propelling a vehicle. However, numerous modules and devices for the vehicle as well as the engine require electrical power. Typically, a rechargeable battery is provided with the vehicle as a basic power supply. The battery power supply system provides direct current (DC) electrical power for starting the vehicle engine and for operating certain DC compatible electrical loads when the vehicle is not running. The battery is recharged to maintain power by an alternator coupled to and driven by the engine when the vehicle is running. Concurrently, the alternator also provides DC electrical power to the vehicle electrical loads.
With the advent of electronics in today's modern vehicle, ground vehicles, boats and aircraft alike, the amount of electrical loads which require power has significantly increased. Moreover, many various auxiliary electrical loads are dependent upon stable alternating current (AC), for example, rescue and military vehicles having AC powered communications equipment. Additionally, many other vehicles, such as utility and telephone company repair and maintenance vehicles and vehicles providing electrical welding equipment, are increasingly utilizing AC equipment dependent upon clean AC power.
Various systems have been proposed for alleviating the complication of operating both AC and DC powered electrical equipment. One such system involves driving an auxiliary AC generator from the vehicle's engine or principal power plant. This can be accomplished by connecting the generator to a power take off or to any other suitable connection to engine output. While this will indeed operate a generator, variations in engine speed will wreak havoc with characteristics of power output and therefore with equipment which is dependent upon stable voltage and frequency characteristics of electrical power.
Accordingly, various systems have been proposed to control speed of an AC generator. One such system utilizes a hydraulic circuit having a proportional valve for supplying a constant rate of fluid flow to a hydraulic motor. The hydraulic motor in turn drives a generator for supplying AC power to certain AC compatible electrical loads. However, such systems can have difficulty maintaining precise frequency output for controlling the most sensitive AC equipment and are often susceptible to premature mechanical failure.